Reactions of unbridged zirconocene dichlorides, (RnC5H5−n)2ZrCl2 (n = 0, 1, or 2), with diisobutylaluminum hydride (HAliBu2) result in the formation of tetranuclear trihydride clusters of the type (RnC5H5−n)2Zr(μ-H)3(AliBu2)3(μ-Cl)2, which contain three [AliBu2] units. Ring-bridged ansa-zirconocene dichlorides, Me2E(RnC5H4−n)2ZrCl2 with E = C or Si, on the other hand, are found to form binuclear dihydride complexes of the type Me2E(RnC5H4−n)2Zr(Cl)(μ-H)2AliBu2 with only one [AliBu2] unit. The dichotomy between unbridged and bridged zirconocene derivatives with regard to tetranuclear versus binuclear product formation is proposed to be connected to different degrees of rotational freedom of their C5-ring ligands. Alkylaluminum-complexed zirconocene dihydrides, previously observed in zirconocene-based precatalyst systems activated by methylalumoxane (MAO) upon addition of HAliBu2 or AliBu3, are proposed to be species of the type Me2Si(ind)2Zr(Me)(μ-H)2AliBu2, stabilized by interaction of their terminal Me group with a Lewis acidic site of MAO.

Brintzinger, Hans-HerbertBaldwin, Steven M.Reactions of unbridged zirconocene dichlorides, (R<sub>n</sub>C<sub>5</sub>H<sub>5−n</sub>)<sub>2</sub>ZrCl<sub>2</sub> (n = 0, 1, or 2), with diisobutylaluminum hydride (HAl<sup>i</sup>Bu<sub>2</sub>) result in the formation of tetranuclear trihydride clusters of the type (R<sub>n</sub>C<sub>5</sub>H<sub>5−n</sub>)<sub>2</sub>Zr(μ-H)<sub>3</sub>(Al<sup>i</sup>Bu<sub>2</sub>)<sub>3</sub>(μ-Cl)<sub>2</sub>, which contain three [Al<sup>i</sup>Bu<sub>2</sub>] units. Ring-bridged ansa-zirconocene dichlorides, Me<sub>2</sub>E(R<sub>n</sub>C<sub>5</sub>H<sub>4−n</sub>)<sub>2</sub>ZrCl<sub>2</sub> with E = C or Si, on the other hand, are found to form binuclear dihydride complexes of the type Me<sub>2</sub>E(R<sub>n</sub>C<sub>5</sub>H<sub>4−n</sub>)<sub>2</sub>Zr(Cl)(μ-H)<sub>2</sub>Al<sup>i</sup>Bu<sub>2</sub> with only one [Al<sup>i</sup>Bu<sub>2</sub>] unit. The dichotomy between unbridged and bridged zirconocene derivatives with regard to tetranuclear versus binuclear product formation is proposed to be connected to different degrees of rotational freedom of their C<sub>5</sub>-ring ligands. Alkylaluminum-complexed zirconocene dihydrides, previously observed in zirconocene-based precatalyst systems activated by methylalumoxane (MAO) upon addition of HAl<sup>i</sup>Bu<sub>2</sub> or Al<sup>i</sup>Bu<sub>3</sub>, are proposed to be species of the type Me<sub>2</sub>Si(ind)<sub>2</sub>Zr(Me)(μ-H)<sub>2</sub>Al<sup>i</sup>Bu<sub>2</sub>, stabilized by interaction of their terminal Me group with a Lewis acidic site of MAO.Bercaw, John E.2008-12-24Alkylaluminum-complexed zirconocene hydrides : identification of hydride-bridged species by NMR spectroscopyterms-of-useengBercaw, John E.Journal of American Chemical Society ; 130 (2008), 51. - S. 17423-174332013-06-19T14:22:29ZBaldwin, Steven M.Brintzinger, Hans-Herbert2013-06-19T14:22:29Z